The free aqueous phase was obtained from individual samples of dental plaque and the plaque matrix was then eluted with a chaotropic buffer in an attempt to remove bound protein. The fluid and the chaotropic phases were assayed for secretory immunoglobulin A (SIgA), IgG, IgM, the third component of complement (C'3), lysozyme, lactoperoxidase and lactoferrin. The presence of these specific and non-specific immune factors in the free and bound phases suggest they are important in host defense at the plaque-enamel interface. Analyses by S.D.S. PAGE and immunoblotting revealed that many of the immune proteins are degraded into small molecular weight fragments. Analysis of specific and innate immune factors in plaque fluid from a subset of Columbian children with markedly different caries experience is largely complete. While there do not appear to be obvious differences in the levels of the immune factors in the free-fluid phase, the cell-bound factors await analysis.